JPH02108722A - Weak ground improving technique - Google Patents

Abstract

PURPOSE:To reduce constructive expenses for improving weak ground by driving any of a number of agglomerating piles, driven into weak ground, up to a relatively deep layer and the remaining piles shallowly among these piles. CONSTITUTION:Concerning the drive of a number of agglomerating piles (P) into weak ground (G), any of piles (P) are first driven up to a relatively deep layer. Next, among these respective piles (P), the remaining piles (P) are driven shallowly. Then, at shallow layer portions where earth quake gives great power, the agglomerating piles (P) are driven in density to build up strong complex ground for preventing liquefaction in earth quake. It is thus possible to reduce constructive expenses for improving weak ground.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application J This invention relates to a soft ground improvement method for preventing liquefaction during an earthquake by creating consolidated piles in the soft ground.

``Conventional technology'' Traditionally, soft ground improvement methods include cement,
The consolidation pile method is known, in which a stabilizing material such as lime is mixed and stirred in the soil to chemically consolidate the soil and create many columnar consolidation piles. One such method is the demic-l construction method.

This Demick-L construction method is a consolidation pile construction method that uses a cement-based hardening material as a stabilizing material.The slurry-like cement-based hardening material is compressed into soft ground and mixed continuously with a stirring shaft. , which improves the structure between soil particles in the ground by hardening it through a hydration reaction and a borazone reaction.

The construction machine used in this DEM construction method is equipped with a rotary drive device at the top, a shaft is connected to this rotary drive device, a stirring blade is attached to the lower end of this shaft, and the above-mentioned cement-based hardening The structure is such that the material passes through the shaft and is discharged from the stirring blades.
Moreover, the above-mentioned shafts are usually used as two axes to increase mixing performance and improve efficiency. The stirring blade of this construction machine usually has a diameter of 1111 mm, which is 0.2 mm.
It is installed in series with one wrap, and an area of approximately 1.5m" can be improved with one installation.

``Problem to be solved by the invention'' By the way, in the above-mentioned consolidation pile construction method, ■ the required strength can be reliably obtained by adding a hardening agent suitable for the soil quality to be improved, and ■ the required strength can be achieved in a short time. ■ It is a low-vibration and low-noise construction method that does not affect the surrounding area; ■ It does not use large amounts of sand like conventional construction methods, so it contributes to resource conservation. ■While it has excellent features such as automatically recording data necessary for construction management (elevating speed and rotation speed of stirring blades, amount of slurry injected, etc.), when preventing liquefaction in the event of an earthquake, a large number of Since it is necessary to create compacted piles densely, there is a drawback that the construction cost increases when the layer of soft ground is thick and the compacted piles have to be driven deep underground.

However, since the seismic force is relatively small deep underground,
Even if the ground is thick and soft, it is thought that there is little risk of liquefaction in the deeper layers, and it is desirable to reduce construction costs as much as possible, especially if the structure to be built on that ground is low-rise. was.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a low-cost method for improving soft ground that is particularly suitable as a measure against liquefaction in low-rise structures.

``Means for Solving the Problems'' The soft ground improvement method of the present invention, when driving a large number of consolidated piles into soft ground, places several consolidated piles to a relatively deep layer. By placing the remaining consolidated piles between each of these consolidated piles at a shallower depth than the above consolidated piles, the consolidated piles are created densely in the shallow part of the soft ground, and the Consolidated piles are created sparsely in the deep layer.

"Operation" In the soft ground improvement method of the present invention, when driving a large number of consolidated piles into soft ground, several consolidated piles are driven to a relatively deep layer, and each of these consolidated piles is By placing the remaining consolidated piles between the consolidated piles at a shallower depth than the above-mentioned consolidated piles, the consolidated piles are densely built in shallow areas where seismic force is large, and a strong composite ground is constructed. Therefore, in the deep layer where seismic force is small, consolidated piles are created sparsely, reducing construction costs.
As a result, construction costs can be reduced while maintaining sufficient liquefaction prevention effects in the event of an earthquake.

"Embodiment" An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

In the soft ground improvement method of this embodiment, as shown in Fig. 1, consolidated piles P are placed at a number of construction positions set vertically and horizontally at predetermined intervals on the soft ground G. Assuming that a consolidated pile P is cast to a relatively deep layer at an arbitrary construction position, the consolidated pile P will be placed at four construction positions adjacent to this consolidated pile P. Also, pour it shallowly. And this solidified bile P
At the construction position adjacent to the construction position, by again driving the consolidated piles P to a deep layer, the consolidated piles P are densely created in the shallow part of the soft ground G, and Then, the solidified biles P are created sparsely.

As a method for creating the solidified pile P, for example, there is a demic-L construction method.

As shown in Figure 2, the main parts of the construction machinery used in this demic-l construction method are the crawler type base machine 1.
It is generally composed of a crawler 2, a working section 3, and a support column 5 supported by a boom 4.

A stirring shaft drive device 6 is supported on the support column 5 so as to be movable up and down by a vertical drive device (not shown), and a pair of hollow cylindrical stirring shafts 7 are attached to the lower end of the stirring shaft drive device 6 on the left and right sides ( They are connected in parallel in the direction (perpendicular to the plane of the paper in FIG. 2). In addition, a cement slurry such as cement mortar or cement milk is supplied as a stabilizing material into the hollow portion of the stirring shaft 7 by a stabilizing material supplying means (not shown).

Next, a case where the soft ground improvement method of the present invention is carried out using the construction machine described above will be explained with reference to FIG.

First, the pair of stirring shafts 7.7 are connected to the stirring shaft driving device 6 (see FIG. 3(a)), and the stirring shafts 7.7 are rotated and lowered by the stirring shaft driving device 6. 7. Penetrate 7 into soft ground G (Fig. 3(b)
)reference). Next, with the stirring shafts 7.7 fully penetrated, a further pair of stirring shafts 7.7 are attached to the upper ends of these stirring shafts 7.7.
(see FIG. 3(c)), and then continue the penetration process as described above.

Then, when the lowest end of the two connected stirring shafts 7.7 descends to a position a predetermined distance from the ground improvement target depth indicated by the broken line in Figure 3 (see Figure 3 (d)). ), a stabilizer such as cement slurry is press-fitted and supplied into the hollow part of the stirring shaft 7 by a stabilizer supply means (not shown). In this way, the stabilizing material supplied to the hollow part in the stirring shaft 7 flows downward and is discharged into the soft ground G from a discharge port (not shown) provided at the lower end of the stirring shaft 7. Then, by further rotating and lowering the stirring shaft 7 and discharging the stabilizing material, the ground soil and the stabilizing material are stirred and mixed (
(See Figure 3(e)).

In this way, the lowest end of the stirring shaft 7 is brought to the ground improvement target depth, and then the stirring shaft 7 is rotated upward (see FIG. 3(r)). Note that even in this state, the stabilizing material is continued to be supplied into the stirring shaft 7 from the above-mentioned stabilizing material supplying means. Then, by discharging the stabilizing material while further rotating the stirring shaft 7 upward, the ground soil and the stabilizing material are stirred and mixed to improve the ground. In this case, the amount of ground soil corresponding to the amount of stabilizer injection will be surplus, but the stirring shaft 7
As the rotation is rising, excess soil S is discharged to the ground due to the influence of the screw blades, etc. (see Figure 3 (g))
.

Then, the stirring shaft 7.7 is raised in this way, and the upper stirring shaft 7 of the two connected stirring shafts 7.7 is completely exposed above the ground.After that, the upper stirring shaft 7 is separated. Connect the drive device 6 to the stirring shaft 7 again (Fig. 3 (h)
reference). Then, by further discharging the stabilizing material from the discharge port at the lower end of the stirring shaft 7 into the soft ground G and rotating the stirring shaft upward, the stirring shaft 7.7 is rotated while mixing and stirring the ground soil and the stabilizing material. It is pulled out to the ground, thereby creating a solidified baile P.

In this example, the consolidated pile P was created using a construction machine with two stirring shafts, but the consolidation pile P could also be created using a construction machine equipped with a -shaft or three or more stirring shafts. good. Furthermore, as a stabilizer, it is not necessarily necessary to use cement slurry such as cement mortar or cement milk; water glass, cement paste, etc. may be used, and quicklime, cement, etc. may be used in powdered form. Alternatively, a thickener such as CMC or bentonite may be added to these materials.

"Effects of the Invention" The soft ground improvement method of the present invention, when driving a large number of consolidated piles into soft ground, places several consolidated piles to a relatively deep layer, and The remaining consolidated piles were placed between the consolidated piles at a shallower depth than the above consolidated piles, so in shallow areas where seismic forces are large, the consolidated piles were built densely to create a strong composite ground. In deep areas where seismic force is small, consolidated piles can be sparsely created to reduce construction costs. can be reduced.

[Brief explanation of the drawing]

1 to 3 are diagrams showing one embodiment of the present invention, and FIG. 1 is an explanatory diagram illustrating a soft ground improvement method;
FIG. 2 is a schematic configuration diagram of a construction machine used in the demi-L construction method, and FIG. 3 is an explanatory diagram for explaining the DEM-L construction method. G: Soft ground, P: Consolidated pile, l: Crawler type base machine, 2...
・Crawler, 3... Working part, 4... Boom, 5... Support column,... Stirring shaft drive device, 7... Stirring shaft , S... Surplus soil.

Claims (1)

[Claims] When driving a large number of consolidated piles in soft ground, some of the consolidated piles are driven to a relatively deep layer, and the remaining consolidated piles are placed between each of these consolidated piles. Soft ground, characterized in that the compacted piles are densely created in the shallow part of the soft ground, and the compacted piles are sparsely created in the deep part of the soft ground, by placing the compacted pile shallower than the compacted pile. Improved construction method.